We have developed formulations of a C31 G-based microbicide which maintains potent anti-bacterial and anti-viral activity when tested with in vitro and animal test systems. In this proposal we will expand our repertoire of surfactant-based formulations and analyze the physical characteristics and release of active drug from these formulations. Subsequently vaginal model systems, based on data obtained from in vivo human studies, will be used to evaluate microbicidal efficacy. (1) What are the characteristics and kinetics of release of active microbicide from C31G and C31G/alkyl sulfate formulations as compared to commercial (N-9) formulations? (2) When a microbicide is introduced into the vagina what are the dynamics of mixing with resident fluids? (3) What is the distribution and substantivity of formulations within the vagina, and what factors influence these events? (4) The results of these experiments will allow us to ask the most important biological question, namely how effective are the microbicide formulations at killing bacterial and vaginal pathogens under conditions that closely mimic the in vivo situation? To address these questions we propose to develop a series of models of increasing complexity, beginning with classical pharmaceutical release method, followed by determining the effects of added cervical, vaginal and seminal fluids. This will permit an evaluation of microbicidal activity under conditions that mimic the local vaginal environment. Key experiments will be replicated in human volunteers and in the human vaginal xenograft model, to determine how close the in vivo measurements reflect the in vivo situation.